This conclusion presents some closing thoughts on the concepts covered in the preceding chapters of this book. The book focuses on the minutiae of scale development, refinement and the logical basis of psychological assessment, and so it seems appropriate to end by putting these issues into a little psychological context and suggesting how scores on psychological tests might best be used to develop theory. It considers whole rationale for trying to measure traits before reaching for a questionnaire or designing a new one. The book is concerned with what the authors try to measure with scales, questionnaires or other devices. It argues that it seems to impact on the way in which personality scales, in particular, are developed and used. The book reminds that psychometric tests and scales are terribly simple. It suspects that the problem is that researchers who design studies are not the ones who actually administer the questionnaires.